Field of the Invention
The invention relates in general to ignition devices and in particular to a new and useful glow plug for motor-independent liquid fuel-fired heaters for motor vehicles and in particular for auxiliary heaters in action when the car is not running as well as for add-on heaters, with a plug base having a heating means on one side and electrical terminals for connection on the other.
In motor vehicles, and, in particular, in trucks and busses, but also in automobiles so-called auxiliary or add-on heaters are installed, which are motor-independent heaters running on e.g. gasoline or diesel fuel. In order to start the heater, i.e. for the ignition of a burner flame, a glow plug is used which is supplied with current just before, or while, air and fuel are supplied to the heater in order to inflame the mixture of air and vaporized gasoline or fuel.
Usually the glow plug is fed by the vehicle battery. The usual glow plugs have a helical wire winding around a rod-shaped carrier having a resistance of only a few ohms but which develops an intense heat when line voltage is applied.
However, the voltage sources for the heaters are different in different motor vehicles. While automobiles usually have a 12 volt battery, the battery voltage in trucks and busses is usually 24 volts. Therefore it was necessary to have two different glow plugs in order to always achieve a certain determined heating output. The stockkeeping of various glow plug types requires undesirable cost and effort, however.
In order to avoid having to stock various glow plug types, it was common to work only with one glow plug, namely with a glow plug for a line voltage of 12 volts. When the heater was installed into a vehicle having a 24 volt battery a multiplier resistor was arranged upstream of the glow plug with the same electrical multiplier resistance value. Due to this a line voltage of 12 volts was achieved at the multiplier resistor as well as at the heating device.
The arrangement of the multiplier resistor, however, required some effort as the same amount of thermal energy generated at the glow plug was also released by the multiplier resistor. In order to divert the heat the multiplier resistor had to be arranged in a place where it did not present a danger for other parts of the vehicle. Other than the space problem the mounting of the multiplier resistor was relatively complicated.